At present, quality and safety are key priorities for the food industry and the authorities, and that is why the current lines of research in Europe are focused specifically to ensure the quality and safety of food.
Obviously, the packing and packaging systems containing and protecting food during all their shelf life are also subject to this trend. In particular, the primary packaging, which is a vital element in ensuring the quality and safety of the packaged product, plays a crucial role in attaining this goal.
Furthermore, it has been found that the amount of discarded products along the supply chain, which could actually be consumed without problems, is worryingly high.
The availability of a system that reports in an individual, non-destructive way and in real-time the quality and safety of food is a complementary and valuable tool for achieving the objectives established by the European Union.
At present, the expiration date is set according to the date of production, so the first thing that is produced is the first thing that should be consumed, regardless of the storage conditions or the initial microbial load of the product, which sometimes causes the product to be discarded when it could really be consumed in perfect condition, or that poisonings occur through the consumption of a spoiled product.
In the prior art different inks are known that change colour with the change of the food's condition.
Thus, the German Patent No. 19605522, year 1996, in the name of KARLSRUHE FORSCHZENT which belongs to the state of the art, refers to a layer that is sensitive to an opto-chemical sensor having a metal complex of phthalocyanine fixed in a porous matrix.
European Patent No. 0449798 in the name of AVL MEDICAL INSTRUMENTS, year 1991, is also known, which refers to a method for quality control of packaged organic substances, preferably packaged food products, tea, coffee, tobacco and medicines, wherein the substances to be examined are brought into contact with a planar optical sensor element which is mounted inside the packaging and reacts to the change in the gas composition in the space above the sample through a change in colour or fluorescence. The change in one of the optical properties of the sensor element is detected visually or optoelectronically.
There are other patents which may be considered, such as US2006057022 “FOOD QUALITY INDICATOR”, year 2005, which refers to an indicator that uses natural pH indicators and reacts to acids such as H2S. It is an indicator that cannot be used in a modified atmosphere.
Within the same group is Patent WO2011045572 “INTELLIGENT PIGMENTS AND PLASTICS”, year 2010, which refers to an indicator such as a melted processed polymer composite for use in food packaging, which is sensitive to CO2, O2 and NH3, with indicators such as m-cresol purple, bromophenol blue, methylene blue, etc., being said dye or ink for coating or impregnating with inorganic pigments such as, SiO2TiO2, Al2O3, MgO, zeolites, which results, in the end, in a water soluble ink. As it uses CO2, it cannot be used in a modified atmosphere.
Thus, Patent WO2009/070760 “HYDROGEN SULFIDE INDICATING PIGMENTS”, year 2008, refers to pigments that react to hydrogen sulphide, with application to environmental security. It is known that metals react to hydrogen sulphide by changing their colour; however, the colour change does not occur gradually nor is directly linked to the concentration of deteriorating compounds of food in controlled atmospheres inside the fresh product packaging.
U.S. Pat. No. 7,153,532, in the name of Johnson Matthey PLC, year 2001, is an antecedent which refers to a sensor for detecting food spoilage or the opening or rupture of the package comprising a metal complex fixed at or on a substrate, which complex is capable of releasing a detectable component.
Given this situation, and in order to ensure the quality and safety of food and decrease the amount of food wasted, it is of interest to provide tools and methods which provide information on the shelf life of food in real time, based on specific aspects of the product, such as for example, microbial load or physical and chemical characteristics, and not on the currently used estimation methods.
The closest document is the cited U.S. Pat. No. 7,153,532. This document primarily addresses the detection of the grade of freshness in packaged foods by an ink composition comprising indicator compounds, resins, solvents and additives. Thus, the change in the optical properties is undergone by the chromophores and/or fluorophores joined to the metal centre, showing a colour change and a change in fluorescence when the product is inedible. In addition, some of the elements used such as titanium or rare earths are not very suitable for the packaging of low cost food, since their cost does not compensate the economic cost of the product. Finally, the referred to document has the following limitations:                it requires an optical element for viewing, and        the indicator developed has included a metal complex whose manufacturing process on an industrial scale is not defined or optimized.        